The present invention is generally related to a high temperature steam valve, and more particularly to a high temperature steam valve employing a cooling mechanism to cool valve constituent elements. The present invention is also related to a steam turbine plant having a high temperature steam valve.
Recently, it is required that steam turbines of thermal electric power plants be more effective in the light of the environmental problems, so that the steam temperature tends to be raised higher. The steam condition now adopted widely is of about 169 kg/cm2 and 566 degrees Celsius, or of about 246 kg/cm2 and 566 degrees Celsius as shown in Japanese Patent Application Publication Hei 7-247806, the disclosure of which is hereby incorporated by reference in its entirety. The highest steam condition is currently 610 degrees Celsius. The reason why these steam conditions are adopted is mainly that materials used for the parts of the steam valves provided to control the steam flow of the steam turbine are restricted on their cost.
As is well known, the steam valve is so constructed that a valve element located opposite to a valve seat in a valve casing can be driven from the outside through a valve rod. This valve rod is supported slidably with a bush in the valve-rod penetrating portion of the valve casing. Some gap is provided between the bush and the valve rod to allow sliding. In the steam turbine unit employing the currently highest steam condition of the steam temperature of 610 degrees Celsius, heat resistant alloyed steel such as 12-Cr steel for the valve casing, nitride steel for the bush and 12-Cr steel for the valve rod are adopted as the materials constituting each member of the steam valve.
Aiming at higher efficiency is a recent trend, and thereby the steam temperature tends to be raised. Therefore, over the current highest steam temperature of 610 degrees Celsius, adoption of a steam temperature higher than 650 degrees Celsius or even 700 degrees Celsius is studied. Although raising the steam temperature is welcome for improving the thermal efficiency of the steam turbine system, it is very severe for the constituent materials of the steam valve. That is to say, the valve rod gets creep deformation, and oxidized scale which inhibits smooth sliding may deposit on the sliding portion between the valve rod and the bush, and moreover may stick the sliding portion between the valve rod and the bush with a high temperature steam existence.
Accordingly, in a conventional high temperature steam valve, a hole is bored inside the valve rod to let cooling steam flow through to cool the valve rod (e.g. Japanese Utility Model Application Publication Sho 57-145879, the disclosure of which is hereby incorporated by reference in its entirety). In another conventional valve, a valve lid of the valve casing is divided into an upper lid and an inner lid to let cooling steam flow between the upper lid and the inner lid to cool the flange of the casing, and an anti-oxidized layer is provided on the sliding portion between the valve rod and the bush to prevent oxidized scale from depositing (e.g. Japanese Utility Model Application Publication Sho 61-14276 and Japanese Patent Application Publication Hei 8-93407, the disclosures of which are hereby incorporated by reference in their entirety). Furthermore, in a butterfly valve adjusting the opening of passage by rotation of the disc-like valve element, the technology, in which a cylindrical jacket is additionally provided with a space on the outer periphery of the valve shaft cylinder, which is penetrated by one end of the valve rod, is known (e.g. Japanese Patent Application Publication 2004-19784, the disclosure of which is hereby incorporated by reference in its entirety). The valve shaft cylinder is a cylindrical portion accommodating the shaft seal parts such as a gland packing or an elastic cushion material. Cooling medium is supplied to the annularly formed space from the outside.
However, in the technology described in the above-mentioned Japanese Utility Model Application Publication Sho 57-145879, only the valve rod can be cooled, and cooling the sliding portion between the valve rod and the bush is not taken into consideration. Consequently, it is insufficient for the measure to prevent oxidized scale from depositing on the sliding portion. On the other hand, the technologies described in Japanese Utility Model Application Publication Sho 61-14276 and Japanese Patent Application Publication Hei 8-93407 can cool the bolts binding the flange of the valve casing and the valve lid, but cannot cool the sliding portion between the valve rod and the bush as in Japanese Utility Model Application Publication Sho 57-145879. As a result, the technologies described in Japanese Utility Model Application Publication Sho 61-14276 and Japanese Patent Application Publication Hei 8-93407 cannot prevent oxidized scale from depositing at a higher temperature steam even if anti-oxidized layers are provided.
Furthermore, because the technology described in Japanese Patent Application Publication 2004-19784 has the structure cooling the shaft seal part rather than the bearing member rotatably supporting the valve rod, heat is transferred from the valve inside to the bearing member i.e. the valve rod sliding portion via the valve rod, and thereby the rod sliding portion cannot be cooled sufficiently. In consequence, the technology described in Japanese Patent Application Publication 2004-19784 also is not sufficient for the measure to prevent oxidized scale from depositing on the valve rod sliding portion which supports rotation of the valve rod.
As mentioned above, the technologies described in the above-mentioned documents will increase abrasion quantity of the valve sliding portion because oxidized scale deposits on the valve rod sliding portion. As a result, the valve rod and others are obliged to be replaced because the sliding gap between the bush and the valve rod cannot be appropriately maintained for a long time.